A great many different types of electrical generators are known and used in different applications. In general, generators include a rotating mechanism known as a rotor which includes permanent magnets or induction coils and is typically positioned internally of a stationary mechanism known as a stator. Rotation of the rotor, often by an external means such as an internal combustion engine, induces electrical current in the stator, which can be used to perform work. Operation of electrical generators tends to produce heat which must typically be dissipated in some manner to avoid overheating the system. One common strategy for cooling electrical generators, and in particular for cooling electrical generator rotors, is to pass air through the generator to dissipate heat. Passive heat dissipation strategies are also known. In some instances, however, conventional cooling techniques are not sufficient or impractical and another strategy such as spraying a liquid like oil or engine coolant onto parts of the generator is used. Oil spray techniques and the like have their own set of drawbacks. In the case of permanent magnet generators, debris carried via the cooling fluid may magnetically adhere to the rotor, eventually affecting its operation.
In addition to effectively cooling generator components, another challenge relates to properly balancing a rotor. Many machine components, and in particular cast machine components of the type commonly used in permanent magnet stators, tend to have inherent variability in the location of the center of mass of a component. In other words, many stators formed of cast material will tend to have a certain degree of deviation in a location of the center of mass from a theoretical geometric center of the component. If the deviation in center of mass issues are not addressed, operation of the generator may be negatively affected. In particular, unbalanced rotors can result in vibrations within the system and premature wear of components such as bearings. Suppliers of rotors have traditionally mounted balancing mass on the rotor core itself. This is commonly achieved by machining bores in the rotor core, then threading mass mounting bolts or the like into the machined bores. Mass can then be selectively mounted on or retained by the bolts to compensate for asymmetry in the mass distribution of the rotor core.
An induction generator having a balancing mechanism and liquid cooling is known from U.S. Pat. No. 6,734,585 B1 to Tornquist et al. The disclosure of Tornquist et al is directed to rotor end caps for a high speed generator. The end caps include a manifold for circulating fluid through the rotor. Induction coils mounted in wedges are retained during operation via the end caps, which also assist via their manifolds in circulating cooling fluid through the wedges. Mass for balancing is inserted into the end caps. While the design of Tornquist et al. may be effective in its intended high speed environment, it is less well suited to generators of certain other designs, and may be prohibitively complex and costly for lower speed environments.